.box {
  margin: 200px auto 0;
  padding: 0;
  width: 400px;
  height: 70px;
  li {
    float: left;
    position: relative;
    width: 50px;
    height: 70px;
    overflow: hidden;
    div {
      position: absolute;
      left: 0;
      top: 0;
      width: 50px;
      height: 140px;
      img {
        float: left;
      }
    }
    span {
      display: block;
      background: url('../img/c.jpg');
      width: 50px;
      height: 70px;
      &.active {
        background: url('../img/b.jpg');
      }
    }
  }
}
